1. Field of the Invention
The present invention relates generally to underwater towed transducer arrays and, more particularly, to a coupling fabricated from a non-metallic, composite material and operable to join adjacent sections of towed transducer arrays while simultaneously reducing towed array self-noise.
2. Description of the Prior Art
Our desire to detect foreign submarines and ships in the face of improving foreign technology has led to the development of ever-increasingly sensitive oceanographic instrumentation operable to, for example, detect or monitor sound underwater. However, the development of improved systems for supporting highly sensitive towed acoustic arrays has not kept pace with the development of the instrumentation itself. As a result, serious problems attributed to mechanical and electrical interaction between the instrumentation and their support systems has been uncovered. In general, a typical towed acoustic array system includes an electrical signal-carrying, weighted cable towed from a vessel, a vibration isolation module connected to the underwater end to the tow cable, an acoustical array containing one or more hydrophones or transducers connected to the vibration isolation module and electrical signal receiving and processing equipment connected with the ship-board end of the tow cable. Each of the transducers in the acoustical array is operable to produce electrical signals responsive to detected sound pressure waves travelling underwater. The electrical signals produced by the transducers pass through the vibration isolation module and the tow cable to the electrical signal receiving and processing equipment located aboard ship. This electrical equipment manipulates the electrical signals received in a well known fashion to determine the range and bearing of an acoustic signal in the ocean.
An example of a support system which has failed to keep pace with improved towed acoustic array systems is the coupling used to join individual sections of the acoustical array. Typically, the acoustical array, or acoustical transducer array, is formed from a series of individual towed array sections joined in end-to-end fashion. The individual sections are joined via metallic couplings, and these metallic couplings have been found to both mechanically and electrically interact with the acoustical array so as to denigrate the quality of the electrical signals that are produced by the array. In particular, these presently used metallic couplings have been found to produce sag between adjacent acoustical array sections due to the negative buoyancy of the metallic couplings themselves. This sag between adjacent sections disrupts the flow of water along the outer surface of the acoustical array at the location of each coupling as the acoustical array is pulled through the water by the tow vessel. This disruption of water flow causes turbulence around each of the couplings and results in an increase in towed acoustical array self-noise. This self-noise, in the form of sound pressure waves, is detected by the transducers in the towed acoustical array along with the sound pressure waves intended to be detected. It is apparent that these sound pressure waves, generated as a result of the negative buoyancy of the metallic couplings used to join a multiplicity of towed array sections, adversely affect the signal to noise ratio of the incoming acoustic signal.
Consequently, there is a need for a coupling operable to join individual towed acoustical array sections which overcomes the difficulties associated with the metallic coupling known and used today. In particular, there is a need for a coupling for joining adjacent towed acoustical array sections which is fabricated from a non-metallic, composite material to greatly reduce sag between adjacent towed array sections and thus reduce the amount of towed acoustical array self-noise.